Cross-Shelf transport by (storm-modified, sandy) hyperpycnal flows in the Eastern Rhenish Massif during the Upper Eifelian, Middle Devonian

High-resolution sedimentary facies analysis on ten profiles (252.24 m total length) reconstructed a complex depositional system characterised by cross-shelf sediment transport via (storm-modified) hyperpycnal flows in the Unnenberg Formation (Upper Eifelian, Middle Devonian) of the Eastern Rhenish Massif. The hyperpycnal-fed prodeltaic shelf system comprised proximal and distal lobe deposits (=hyperpycnal subaqueous delta) as well as deltaic mid-ramp deposits (=hyperpycnal littoral delta). Facies associations indicated that the hyperpycnal flows were fluctuation, resulting in the development of cyclic sequences of massive, laminated, and rippled sandstones. Plant-rich intervals provide a clear link to terrestrial sources. Hummocky cross-stratification, quasi planar-lamination and combined-flow ripples, suggest combined flow influences, driven by monsoonal dynamics. The presence of elementary depositional sequences (1.5–11 m thick) indicate progradational trends related to climate-driven hyperpycnal processes. Sedimentation rates of 0.15–1.12 m/kyr align with a monsoon-regulated half-precession cycle of 9.8 kyr, suggesting a direct link between climatic forcing and sediment delivery. This research supports the role of hyperpycnal flows in transferring sandy sediments across continental shelves, reinforcing their importance in constructing clastic deltaic ramps and shelfal lobes during the Middle Devonian. The findings contribute to our understanding of sedimentary dynamics in ancient marine systems and highlight the importance of hyperpycnal flows as a key mechanism in sediment distribution from deltaic to deep-marine environments.